Microwave switch



Jan. 16, 1962 G. w. LUKE 3,017,585

MICROWAVE SWITCH Filed April 24, 1959 INVENTOR. GEORGE W LUKE A TTORNE Y8 tstl ????5 Patent 0 York Filed Apr. 24, 1959, Ser. No. 808,743 4 Claims. (Cl. 333-7 The present invention relates to microwave transmitting and receiving equipment and more particularly to an improved switch capable of efiiciently diverting microwave energy from one branch to another branch of a waveguide section.

Prior art microwave switches when cascaded are frequency sensitive, requiring spacing in wavelengths or fractions thereof. Moreover, prior art switches usually consist of a single diode mounted in a simple waveguide. These switches, when short-circuited by the application of a D.C. voltage to the diode, merely reflect energy back along the waveguide.

An object of the invention is the production of a microwave switch which will efficiently divert energy from one branch to another branch of the waveguide section.

Another object of the invention is to produce a microwave switch that will not be frequency sensitive when cascaded.

A further object of the invention is to produce an extremely fast-acting switch having a switching time of the order of one millimicrosecond.

These and other objects and advantages of the present invention will be readily apparent from the following detailed description when considered in connection with the accompanying drawing, in which:

The figure of the drawings is a perspective view, partially broken away, showing the improved microwave switch.

The microwave switch of the present invention is shown in the figure. The basic unit is comprised of the standard rectangular waveguides 10 and 12 joined along the E plane with a section of the common wall 14 removed to define a slot or coupling space 16. There is thus formed four waveguide sections A, B, C, and D.

In the slot 16 there is disposed a pair of germanium crystals 18 and 20 which are located symmetrically in this slot and separated by a space of approximately one quarter of a wavelength. These crystals may be of type which are commercially available and designated as IN263.

A source of voltage is suitably coupled to the crystals 18 and 20 through the leads 22. and 24 which are adapted to pass through holes formed in the upper wall of the waveguide sections 10 and 12. preferably along the line of the common wall portion 14.

The operation of the switching device illustrated in the figure of the drawings is as follows:

In absence of an energizing signal to the crystals 18 and 20, they will present a pure resistance to the RF field established by a microwave input signal at A. With a fixed input microwave signal level at A, a maximum signal level will appear at B, a minimum signal level will appear at C and D, and a minimum reflection to the input A. The action of the system thus far described may be considered as a conventional slot coupler with a shorted slot, hence all power is transferred along the primary waveguide 10 from the input A to the output B.

Upon the application of an energizing pulse to the crystals 18 and 20, they will present a pure capacitance to the RF field established by a microwave input signal at A. In the energized state the crystals 18 and 20 will conduct heavily in the forward direction and thereby reduce the impedance of the slot 16 to a value approach- ICC ing the characteristic impedance of the waveguide. If the coupling coetficient of the system is two, then minimum power will appear at D and the input power will divide equally between B and C. However, in the event the slot 16 is over-coupled so that the coupling coefiicient is unity then all of the output power will appear at C.

The exact theory and phenomena which occurs within the above described system is not fully understood; howover, all investigations thus far conducted indicate that the bandwidth of the switch is inherently centered at approximately 9700 me. p.s. regardless of the physical length of the slot or height and width of the waveguide, for the IN263 diode used in the investigations.

A switch constructed in accordance with the invention has the following characteristics for 0 dbm input at A.

(a) 8 dbm'at B (b) 2 dbm at C (c) 30 dbm at D (d) Input VSWR, 1.3

It is expected that the power at C for the pulse on condition will eventually be increased to 0.5 dbm.

Maximum switching range is obtained if the crystals are initially reverse-biased to zero current flow in the presence of the applied RF field.

Both germanium and silicon crystals have been used. The characteristics are found to be reversed in that the silicon crystal is conducting when the switch is off and the germanium is conducting only when the switch is on. The performance of germanium is also consider-ably superior to silicon.

It is believed that this type of switching can be extended to microstrip techniques.

According to the provisions of the patent statutes, I have explained the principles and mode of operation of my invention, and as illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. In a microwave switch, a pair of waveguide sections arranged in side-by-side relationship and having a common wall, said wall being formed with a slot providing communication between the sections, and a pair of diodes in the slot in spaced relation to each other and to the walls defining the slot, transfer of electrical energy between the sections through the slot being eifected by the application of electrical pulses to the diodes.

2. A microwave switch as defined in claim 1 wherein said diodes are germanium.

3. A microwave switch as defined in claim 1 wherein said diodes are silicon.

4. A microwave switch comprising primary and secondary waveguide sections arranged side-by-side and having a common wall formed with a slot between the sections, said primary section having an input branch and an output branch and said secondary section having output branches, a pair of crystal diodes mounted in the slot, said diodes being separated by a space of approximately one quarter wavelength, and means for applying energizing potentials to said diodes, said primary waveguide conducting maximum energy applied to its input branch to its output branch under a condition of Zero pulse voltage input to the diodes, said energy output being 3 4 divided between the primary Waveguide output branch References Cited in the file of this patent and the adjacent secondary waveguide output branch, UNITED STATES PATENTS and with minimum reflection to the secondary output branch adjacent the primary input branch, upon the 2557180 Fiske June 1951 2,652,541 Cutler Sept. 15, 1953 application of a positive pulse to the diodes and with a 5 4 coupling coeificient of 2, said energy output appearing Farr, 1957 in its entirety at said adjacent secondary Waveguide out- 2934658 LEWIS 1960 put branch when said slot coupling coefiicient is unity. 

4. A MICROWAVE SWITCH COMPRISING PRIMARY AND SECONDARY WAUVEGUIDE SECTIONS ARRANGED SIDE-BY-SIDE AND HAVING A COMMON WALL FORMED WITH A SLOT BETWEEN THE SECTIONS, SAID PRIMARY SECTION HAVING AN INPUT BRANCH AND AN OUTPUT BRANCH AND SAID SECONDARY SECTION HAVING OUTPUT BRANCHES, A PAIR OF CRYSTAL DIODES MOUNTED IN THE SLOT, SAID DIODES BEING SEPARATED BY A SPACE OF APPROXIMATELY ONE QUARTER WAVELENGHT, AND MEANS FOR APPLYING ENERGIZING POTENTIALS TO SAID DIODES, SAID PRIMARY WAVEGUIDE CONDUCTING MAXIMUM ENERGY APPLIED TO ITS INPUT BRANCH TO ITS OUTPUT BRANCH UNDER A CONDITION OF ZERO PULSE VOLTAGE INPUT TO THE DIODES, SAID ENERGY OUTPUT BEING DIVIDED BETWEEN THE PRIMARY WAVEGUIDE OUTPUT BRANCH, AND THE ADJACENT SECONDARY WAVEGUIDE OUTPUT BRANCH, AND WITH A MINIMUM REFLECTION TO THE SECONDARY OUTPUT BRANCH ADJACENT THE PRIMARY INPUT BRANCH, UPON THE APPLICATION OF A POSITIVE PULSE TO THE DIODES AND WITH A COUPLING COEFFICIENT OF 2, SAID ENERGY OUTPUT APPEARING IN ITS ENTIRELY AT SAID ADJACENT SECONDARY WAVEGUIDE OUTPUT BRANCH WHEN SAID SLOT COUPLING COEFFICIENT IN UNITY. 